Role for tumor necrosis factor as mediator of lung injury following lower torso ischemia

Ischemia and reperfusion of the ischemic lower torso lead to a neutrophil- (PMN) dependent lung injury characterized by PMN sequestration and permeability edema. This mimics the injury seen after infusion of tumor necrosis factor α (TNF), a potent activator of PMN and endothelium. This study tests whether TNF is a mediator of the lung injury after lower torso ischemia. Anesthetized rats underwent 4 h of bilateral hindlimb tourniquet ischemia, followed by reperfusion for 10 min, 30 min, 1, 2, 3, and 4 h (n = 6 for each time point). Quantitative lung histology indicated progressive sequestration of PMN in the lungs, 25 ± 3 (SE) PMN/10 high-power fields (HPF) 10 min after reperfusion vs. 20 ± 2 PMN/10 HPF in sham animals (NS), increasing to 53 ± 5 PMN/10 HPF after 4 h vs. 23 ± 3 PMN/10 HPF in sham animals (P < 0.01). There was lung permeability, shown by increasing protein accumulation in bronchoalveolar lavage (BAL) fluid, which 4 h after reperfusion was 599 ± 91 vs. 214 ± 35 μg/ml in sham animals (P < 0.01). Similarly, there was edema, shown by the lung wet-to-dry weight ratio, which increased by 4 h to 4.70 ± 0.12 vs. 4.02 ± 0.17 in sham animals (P < 0.01). There was generation of leukotriene B₄ in BAL fluid (720 ± 140 vs. 240 ± 40 pg/ml, P < 0.01), and in three of six rats tested at this time TNF was detected in plasma, with a mean value of 167 pg/ml. TNF was not detectable in any sham animal. Additional rats were subjected to ischemia and were treated intravenously with a polyclonal rabbit antimurine TNF antiserum 30 min before reperfusion (n = 8) or control serum (n = 5). The TNF antiserum, but not the control serum, reduced lung PMN sequestration, limited permeability and edema, and prevented the rise of leukotriene B₄ in BAL fluid (all P < 0.05). These data indicate that TNF is a mediator of the lung injury that follows lower torso ischemia.